1. Field of the Invention
The present invention relates to an electrode structure of a gyrocompass which includes a gyrosphere incorporating a rotor and floating in a liquid tank filled with an electrolyte, and a plurality of electrodes disposed in the gyrosphere and the liquid tank, respectively opposed through the electrolyte, wherein at least one circuit for supplying electric power to the rotor involves the electrodes.
2. Description of the Related Art
The following publication is known as a document relating to the gyrocompass having a traditional structure.
“konpasu to jairo no riron to jissai (Theory and practice of compass and gyro)” published on Oct. 1, 1971 by Kaibundou Shuppan Kabushiki Kaisha; Authors: Torao MOZAI and Minoru KOBAYASHI
FIG. 5 is a cross-sectional view illustrating a general configuration of a gyrocompass having a center pin. Reference numeral 1 denotes a computation and follow-up control unit which is a portion which controls the power supply of the apparatus and various arithmetic operations and is in charge of follow-up control for maintaining the relative angle between a gyrosphere and a liquid tank by detecting the position of the gyrosphere. The computation and follow-up control unit 1 mainly consists of a gear mechanism for follow-up and printed board circuits.
Reference numeral 2 denotes a vibration proofing mechanism for maintaining a liquid tank unit substantially horizontally by inclination like a pendulum and for absorbing the vibrations of a ship in the longitudinal and transverse directions of the ship.
Reference numeral 3 denotes a liquid tank unit which is suspended in the vibration proofing mechanism 2. In the liquid tank unit 3, a liquid tank 4 has a gyrosphere 5 and an electrolyte (supporting liquid) 6 incorporated therein. The gyrosphere 5 has a rotor (gyro rotor) 7 incorporated therein, and floats in the liquid tank 4 by means of the electrolyte 6, and its central portion is rotatably supported by a center pin 8 provided in an upper portion of the liquid tank.
FIG. 6 is a perspective view illustrating a feeding structure for the gyrosphere 5. In the traditional structure, the center pin 8 rotatably supports the gyrosphere 5, energizes the interior of the gyrosphere 5 through mercury disposed at its tip portion, and forms one circuit of a feeding route to the rotor 7.
As a structure which does not use a harmful substance such as mercury in consideration of the environment, a structure has been proposed in which, as shown in FIG. 6, the center pin 8 is made to only support the gyrosphere 5, and, as the feeding route to the rotor 7, a belt-shaped electrode 200 on a liquid tank side, which is disposed in such a manner as to oppose through the electrolyte a belt-shaped electrode 100 provided on an outer periphery of an equatorial portion of the gyrosphere 5, is made to function as one feeding route of an external power supply 10. It should be noted that the other feeding route of the external power supply 10 is the same as in the conventional case, and uses dish-shaped electrodes 300 and 400 disposed in face-to-face relation at the bottoms of the gyrosphere and the liquid tank, respectively.
In the case of this structure, the belt-shaped electrode 100 on a gyrosphere side forms a Wheatstone bridge circuit in cooperation with a pair of follow-up electrodes on the liquid tank side (not shown in FIG. 6), and also serves as an electrode for follow-up control together with the electrode for feeding. By virtue of this structure, there is an advantage in that harmful substances such as insulating oil and mercury provided at the tip portion of the conventional center pin.
FIG. 7 is a perspective view illustrating as a set the electrodes on the gyrosphere 5 side and the electrodes on the liquid tank 4 side concerning the electrode structure of the gyrocompass based on such a design concept. Numerical values of angles given in the drawing are given by way of example. Since the respective electrodes are given new appellations, they will be described below.
The belt-shaped electrode 100 on the gyrosphere 5 side consists of one central belt-shaped electrode 101 and a pair of two-rowed electrodes 102 and 103. The central belt-shaped electrode 101 is disposed at an equatorial portion on the side surface of the gyrosphere with a predetermined width in the latitudinal direction and with a length extending slightly less than about half around the gyrosphere (its end point being 2° short in terms of the angle in the drawing) between the positions of follow-up electrodes 17a and 17b on the liquid tank side.
The two-rowed electrodes 102 and 103 are formed on an outer peripheral surface opposite to the central belt-shaped electrode 101 in such a manner as to be spaced apart a predetermined distance with the equator located therebetween on the side surface of the gyrosphere and with a length extending slightly less than about half around the gyrosphere (their end points being 20° short in terms of the angle in the drawing).
The belt-shaped electrode 200 on the inner wall surface of the liquid tank consists of a total of four two-rowed electrodes including a pair of two-rowed electrodes 201 and 202 and a pair of two-rowed electrodes 203 and 204. The two-rowed electrodes 201 and 202 are disposed on the inner wall surface of the liquid tank in such a manner as to be arranged in face-to-face relation to the central belt-shaped electrode 101 on the gyrosphere side while keeping a predetermined distance therebetween in the latitudinal direction and with a length extending slightly less than about half around the inner wall of the liquid tank (their end points being 23° short in terms of the angle in the drawing).
The two-rowed electrodes 203 and 204 are formed on the inner wall surface of the liquid tank opposite to the two-rowed electrodes 201 and 202, have a length extending slightly less than about half around the inner wall of the liquid tank (their end points being 23° short in terms of the angle in the drawing), and are arranged in close proximity to and in face-to-face relation to the two-rowed electrodes 102 and 103 on the gyrosphere side through the electrolyte 6.
The dish-shaped electrodes 300 and 400 are formed on the bottom of the liquid tank 4 and the bottom of the gyrosphere 5, and are disposed at positions where they are located in close proximity to and in face-to-face relation to each other through the electrolyte 6.
By virtue of the above-described electrode structure, the mutually opposing belt-shaped electrodes (the central belt-shaped electrode 101 on the gyrosphere and the two-rowed electrodes 201 and 202 on the liquid tank) are capable of assuming large opposing areas in the equatorial portion, and are therefore capable of feeding a sufficient current for driving the rotor 7 if the electrolyte 6 is present in the gap.
In addition, electrolyte resistors Ra and Rb between both ends of the central belt-shaped electrode 101 and the follow-up electrodes 17a and 17b on the liquid tank side are formed into a Wheatstone bridge, follow-up control of the liquid tank with respect to the gyration of the gyrosphere becomes possible as in the conventional case.
FIG. 8 is a circuit diagram illustrating one example of a deviation detecting mechanism which is applicable to the electrode structure in FIG. 7 in the follow-up control for causing the liquid tank 4 to follow up the gyration of the gyrosphere 5. The circuit in which the follow-up electrodes 17a and 17b are connected to both ends of a primary winding of a transformer 19 is similar to a conventional bridge circuit (not shown), but differs in that one side of the external power supply 10 is not a dish-shaped electrode as in the conventional circuit but is connected to the two-rowed electrodes 201 and 202 on the liquid tank side.
In FIG. 8, the arrangement of the respective electrodes corresponds to a case in which a cross-sectional view of the liquid tank unit is viewed from above. The two-rowed electrodes 201 and 202 on the liquid tank side and the central belt-shaped electrode 101 on the gyrosphere side are opposed to each other with a relatively large area, and the electrolyte resistance therebetween is either small or of such a magnitude as to be negligible in the operation of the follow-up circuit.
In addition, the two-rowed electrodes 201 and 202 have a smaller spread (angle) than the central belt-shaped electrode 101. The electrolyte resistors Ra and Rb which are present between the ends of the central belt-shaped electrode 101 and the follow-up electrodes 17a and 17b on the liquid tank side function as bridge resistors and form a complete Wheatstone bridge together with the transformer having a center tap in the drawing.
In the above-described configuration, in a case where the gyrosphere 5 has gyrated (rotated) in the direction of arrow P, one follow-up electrode 17a and one end of the central belt-shaped electrode 101 approach each other, while the other follow-up electrode 17b and the other end of the central belt-shaped electrode 101 move away from each other. Therefore, the electrolyte resistors Ra and Rb which are present in the gap mutually change differentially, so that the Wheatstone bridge is set in a state of imbalance.
As for a deviation signal E obtained by amplifying the signal from the Wheatstone bridge induced in a secondary winding of the transformer 19 as a result of this imbalance, its amplitude serves as a deviation angle, and its phase indicates the direction of gyration. It should be noted that the belt-shaped electrodes on the gyrosphere side are provided with different shapes concerning the central belt-shaped electrode 101 and the two-rowed electrodes 102 and 103 is in consideration of ensuring that the follow-up point will not be formed at a 180° inverted point.
The belt-shaped electrodes adopted in the gyrocompass having a traditional structure has the following problems in fabrication:
(1) Problems in the Case of Application to Gyrosphere
In the structure of the belt-shaped electrode which has been in use since before the war, for the convenience of allowing electricity to flow by causing the electrodes to float in the electrolyte whose major agent is benzoic acid, electrodes made of carbon or graphite rubber which is resistant against chemicals have been used.
Since these carbons are not necessarily low in electrical resistance, improvement is made to reduce the electrical resistance by using an electrically conductive adhesive and attaching it onto a core metal which is a spherical shell of the gyrosphere. Meanwhile, an insulating lining is provided on the surface of the gyrosphere other than the electrodes by using ebonite rubber or epoxy resin. However, there has been a problem in that the electrolyte penetrates a boundary between the electrode and the insulating lining over time, so that internal conductors are corroded.
(2) Although the diameter of the gyrosphere which has been used since before the war is 252 mm, the diameter is presently 161 mm in view of demand for a compact size. Light weight is essential in terms of securing buoyancy in the electrolyte, and advancement has been made in the conventionally thick-layered insulating lining toward thin film technology employing such as epoxy powder coating. Meanwhile, carbons and the like are relatively fragile materials, and it is difficult to make them thin in proportion to the fact that the shape of the gyrosphere has become small.
As a result, if the belt-shaped electrodes of the traditional structure are applied to the gyrosphere of a new design, it is impossible to maintain buoyancy, and the electrolyte is more likely to penetrate the boundary between the electrode (carbon or the like) and the thin coating, resulting in a decline in reliability.
(3) Since the number of the belt-shaped electrodes used is as many as three and the manufacturing process is complicated, the product is expensive.
(4) Problems in the Case of Application to the Liquid Tank
Although the belt-shaped electrodes of the traditional structure have been in use since before the war, in the case of the liquid tank as well, for the convenience of allowing electricity to flow across the gyrosphere through the electrolyte whose major agent is benzoic acid, electrodes made of carbon or graphite rubber which is resistant against chemicals have been used. Since these carbons are not necessarily low in electrical resistance, improvement is made to reduce the electrical resistance by using an electrically conductive adhesive and attaching it onto the inner surface of the liquid tank made of an aluminum casting in the same way as the gyrosphere.
However, in the light of demand or a compact size and low cost, the present day liquid tank is generally molded from plastics. If the liquid tank is made of plastics, the conventional process for manufacturing the belt-shaped electrode cannot be used at all.
(5) Since the number of the belt-shaped electrodes used is as many as four and the manufacturing process is complicated, the product is expensive and has low reliability.